I. Field of the invention
The present invention relates to flexible layered material which is simultaneously self luminating and capable of reflecting light from an outside source. In one embodiment, the material may be in sheet form comprising an overlying layer of prismatic light reflecting material and an underlying layer of luminescent material in which the latter can be selectively energized to become luminous. The material functions independently of a change in its surroundings, such as the presence or absence of an external light source, and will continue to be fully operational even when the surroundings change.
II. Description of the Prior Art
Various reflective materials are commonly employed for safety and decorative purposes. One of the most common principles employed is simply to apply a reflective coating upon a surface of the item or to construct the item of a highly reflective material such as polished metal. In addition to reflective coatings and specular surfaces, it is also common to use structures which have upon one or both surfaces various formations which reflect the light rays impinging thereon, either principally as a result of the steepness of the angle at which the light ray impinges the surface or by virtue of reflective coatings on the surface of the formations.
There has been a constant demand for retroreflective materials, i.e. materials capable of reflecting the bulk of the light rays impinging thereon in a substantially parallel path back toward the source of the light. Minnesota Mining and Manufacturing Company has sold a material under the trademark SCOTCHLITE which relies upon minute glass spheres embedded in a matrix of synthetic resin to provide such retroreflection. Another type of retroreflective element has been a molded member having cube corner formations on one surface thereof, such molded members being formed from glass or synthetic plastic.
Cube corner reflectors molded from glass and more recently from acrylic resins have commonly been employed as safety devices on bicycles, automobiles and other vehicles. Although it had long been suggested that the cube corner might be of small dimension until the advent of the U.S. Pat. No. 3,684,348, to Rowland, generally such formations were of appreciable size. Furthermore, the nature of the material from which reflectors were fabricated resulted in structures which were relatively rigid in character and which did not lend themselves either to shaping to various substrates of nonplanar character or to use as a fabric which might be worn. Moreover, it came to be recognized that as the size of the cube corner formations is reduced, criticality in control of angles and dimensions becomes far more acute since even a minute deviation will produce a substantial deviation in the capability of the material to retroreflect light rays impinging thereon.
The Rowland patent represented a significant advancement in the field of reflective materials. That patent discloses a retroreflective composite synthetic plastic material comprised of a body portion having substantially smooth surfaces on opposite sides thereof and a large number of minute cube corner formations closely spaced about and projecting from one of the smooth surfaces. The cube corner formations each have three faces and a base adjacent the body portion with a side edge dimension said to be not more than 0.025 inch and preferably less than 0.010 inch and the close spacing avoids any substantial smooth areas therebetween. The body portion and the cube corner formations are separately formed from essentially transparent synthetic plastic resin and are bonded together into a composite structure wherein those light rays entering into the material through the opposite surface of the body portion predominately pass through the body portion and into the cube corner formations by which they are reflected back through the composite structure substantially parallel to the path of entry.
In the most conveniently formed structure of the patented concept, each cube corner formation has one face parallel to one face of every other cube corner formation. Preferably, the cube corner formations are substantially equal in size and arranged in a pattern of rows and columns. The center-to-center spacing between cube corner formations in every row and between cube corner formations in every column is in accordance with a uniform pattern to insure close spacing of the formations and good retroreflection. The apex of each cube corner formation is in alignment with the apices of all of the cube corner formations located in the pattern row and column in which it is disposed, and each apex is vertically aligned with the center of its base.
To provide optimum reflectivity, the composite material has a reflective coating deposited on the cube corner formations. An adhesive layer may then be provided on the reflective coating and a removable piece of sheet material loosely adhered to the adhesive layer. This self-adherent composite structure may be readily used since the sheet material may be removed to adhere the retroreflective sheet material to a substrate. In the optimum form, either with or without an adhesive coating, the reflective coating is metallic and the structure includes a layer of resin deposited on the metallic coating to provide protection therefor. In the absence of a protective resin layer, it is customary to provide an integral, non-removable backing sheet to provide protection for the cube corner formations which can be easily damaged. The backing sheet also serves to enhance the reflectability of the cube corner formations.
Over the years, there have also been significant advances in the use of luminous materials for compositions to provide visibility at nighttime or in locations in which little or no light is available or permissible. Throughout this disclosure, the expression "luminous material" or "luminous composition" is intended to include any material or composition which has phosphorescent, fluorescent, and/or auto luminescent properties. An early disclosure of a luminous device is provided in U.S. Pat. No. 1,373,783 to Willis which discloses a glass plate mounted in a metal holder with a layer of luminous powder compressed between the glass plate and the holder. In a further development disclosed in U.S. Pat. No. 2,333,641 to Corwin, luminous adhesive sheet or tape material is disclosed. In this instance, a sheet of cellulose film is provided with a permanently tacky, pressure-sensitive, adhesive coating containing a luminous material. The coating is applied to one surface of the sheet or tape and is visible through the sheet or tape when the latter is applied to a supporting object.
Still another disclosure of a luminous structure is provided in U.S. Pat. No. 3,260,846 to Feuer which discloses a light source utilizing the beta ray energy of a radioactive material characterized by having a front phosphor region of sufficient depth to absorb the emitted beta rays but not the light generated by the radioactive excitation of the phosphor particles. It includes a back heavy metal reflecting region which, due to the high atomic number, at least 45, serves to back scatter the beta particles as well as reflect light. The reflected beta particles then further excite the forward phosphor regions and ultimately this energy is discharged from the system in a form of light energy.
A more recent development is a phosphorescent type material produced and sold by Hanovia Division of Conrad Inc. of Newark, N.J. under the trademark "SPOT-LITE". In this instance, the luminescent material is of flexible vinyl plastic film which absorbs energy from any light source to which it is exposed, whether natural sunlight, or artificial incandescent or fluorescent light, and chemically generates a luminous light in response thereto. The film produces an intense bright green glow which is visible in absolute darkness for a duration of approximately thirty minutes. After that period of time, even though eighty to eighty-five percent of its luminosity will have diminished, it continues to exhibit a visible glow for up to an additional eight hour period of time. Nonetheless, after exposure of three to ten seconds of ambient light, the film can be recharged to its maximum capacity.
Still more recently, in commonly assigned U.S. application Ser. No. 07/890,391 filed May 26, 1992 entitled "Visibility Enhancing Material", A. Spencer et al. disclosed flexible visibility enhancing material which combines the advantages of a light reflective component and a luminescent component. The material includes a first layer of prismatic light reflective plastic material having an underlying surface formed with a plurality of minute prism-like formations projecting therefrom at regular spaced intervals and an overlying substantially smooth light transmissive surface. Bonded as by heat sealing to the first layer is a second layer of plastic luminescent material contiguously and integrally attached to the underlying surface of prism-like formations and generally coextensive therewith. The visibility enhancing material simultaneously radiates luminescent light from the second layer through the underlying surface of prism-like formations and through the smooth light transmissive surface and reflected light from the prism-like formations through the smooth light transmissive surface.
The combination of the two vinyl layers thereby created a new material which had the characteristics of both. The retroreflective phosphorescent type material of the invention reflected light back in the direction of its source and also produced its own light in conditions of subdued light and total darkness. This unique combination enabled the material of the invention to be visible when light was shined onto it, and also when the light source was extinguished entirely. Additionally, the visibility enhancing material of the invention was visible under extreme variations and lighting conditions, including total darkness. This was an unexpected phenomenon since the construction of the retroreflective material disclosed in U.S. Pat. No. 3,684,348 and marketed under the trademark "REFLEXITE" was not previously known to be transparent or translucent to any substantial extent. It was reflective of light shined onto it, but was not known for any characteristic which would enable transmission of light from a second source on a side opposite the source being reflected. Another unexpected phenomenon provided by the material of the invention was that the life expectancy of the radiance from the luminescent material had been found to be substantially extended.
In a further development, as disclosed in commonly assigned U.S. application Ser. No. 07/890,392 filed May 26, 1992 entitled "Material With Enhanced Visibility Characteristics", the underlying layer of luminescent material can be selectively energized to become luminous.
In still a further development, as disclosed in commonly assigned U.S. application Ser. No. 07/954,387 filed Sep. 30, 1992 entitled "Layered Reflecting and Luminous Material", the layers of prismatic light reflecting material and luminescent material are joined at a first region of finite width as by heat sealing, ultrasonic welding, sewing, or stapling into a unitary structure such that the prism-like formations are substantially destroyed. A second region is thereby defined at which the first layer and the second layer are physically distinct. In the second region, the layered material simultaneously radiates luminescent light from the second layer through the underlying surface of prism-like formations through the smooth light transmissive surface and reflected light from the prism-like formations through the smooth light transmissive surface of the first layer. Only phosphorescent light radiates from the first region. In another embodiment of that invention, the second layer may be replaced with a layer of luminescent material which can be selectively energized to become luminous.